Abstract
Magnetic dipole (MD) transitions are important for a range of technologies from quantum light sources and displays to lasers and bio-probes. However, the typical MD transitions are much weaker than their electric counterparts and are usually neglected in practical applications. Herein, we experimentally demonstrate that the MD transitions can be significantly enhanced by the well-developed magnetic metamaterials in the visible optical range. The magnetic metamaterials consist of silver nanostrips and a thick silver film, which are separated with an Eu3+:polymethyl methacrylate (PMMA) film. By controlling the thickness of the Eu3+:PMMA film, the magnetic resonance has been tuned to match the emission wavelength of MDs. Consequently, the intensity of MD emission has been significantly increased by around 30 times at the magnetic resonance wavelength, whereas the intensity of electric dipole emission is well-preserved. The corresponding numerical calculations reveal that the enhancement is directly generated by the magnetic resonance, which strongly increases the magnetic local density of states around the MD emitter and can efficiently radiate the MD emission into the far field. This is the first demonstration, to the best of our knowledge, that MD transitions can be improved by an additional degree of magnetic freedom, and we believe this research shall pave a new route towards bright magnetic emitters and their potential applications.

Note:
The authors thank the National Natural Science Foundation of China (No. 11374078), the Shenzhen Fundamental Research Projects (Nos. JCYJ20160301154309393, JCYJ20160505175637639, and JCYJ20160427183259083), the Public Platform for Fabrication and Detection of Micro- & Nano-Sized Aerospace Devices, and the Shenzhen Engineering Laboratory on Onganic-Inorganic Perovskite Devices for financial support.